This proposal requests funding for the acquisition of a Flow Cytometer (with sorting capabilities) for several investigators in the Department of Comparative & Experimental Pathology, University of Florida. The research of these investigators centers on the function of various biological agents such as viruses, toxins, hormones, and immune regulators and the interaction with their respective receptors on cell surfaces, as well as identification and quantification of antigens/markers expressed on the surfaces of cells. Our current efforts are handicapped by lack of access to fast, sensitive techniques to study such interactions at the single cell and/or the molecular level. Although many of the agents that are being studied are only present in the body in minute quantities, our efforts to study their mode of action have received a considerable boost through the availability of material produced by several biotechnology firms using DNA recombinant techniques. Ready access to a flow cytometer would allow us to study the functional activity of such reagents at the single cell level with a time resolution that is impossible to achieve with standard sampling techniques using total cell populations. Future experiments we have planned are also dependent on the production of monoclonal antibodies as specific and unique markers for the various cells and their different receptors. With the aid of such markers the interplay and regulation of different cells and different cellular functions can be analyzed. Although the production of monoclonal antibodies has become a routine technique in our department, the isolation, characterization and maintenance of hybrid clones producing specific antibodies is a time consuming process. A flow cytometer drastically reduces the time required to search for and maintain the production of monoclonal antibodies with the desired specificity because its sorting capabilities shortens the selection and cloning procedures.